The present invention relates to a composition used for the treatment of surfaces of flat articles. A surface of a flat article treated with the composition forms a predetermined separation point in a plurality of at least partly superimposed flat articles, i.e. a predetermined point where the plurality of superimposed flat articles can be selectively separated. The flat articles are, for example, made from paper, cardboard, fabric, felt or plastic. The plurality of flat articles to be separated may be a multi-page printed product of paper, plastic or cardboard, which is to be opened at a given point, or may be a stack or scale formation of printed products or flat articles of cardboard, fabric, felt or plastic from which a specific number of articles to be removed by separation at a predetermined point.
Superimposed, flat articles are frequently separated from one another by shoving a separating element such as a separating wedge between the articles to be separated. The more congruent, thin and sensitive to mechanical damage the articles in question are, the more difficult it is to successfully effect a separation using a separating element. On the one hand, it is difficult to aim the element precisely at a predetermined point and, on the other hand, the risk of the separating element damaging the narrow sides or edges of the flat articles is not negligible.
Therefore, superimposed, flat articles are advantageously displaced against one another parallel to their principal surfaces, prior to an effective separation. By such displacement, areas of the principal surfaces of individual articles are exposed, which areas are much better suited for being acted on by a mechanical separating element than the narrow side areas of the articles.
CH-440339 describes a method for displacing relative to each other two directly superimposed articles within a plurality of superimposed articles wherein a displacement force having a component parallel to the principal surfaces of the articles is employed. In this method, there is no action on individual narrow sides or edges of the articles. To enable the mentioned displacement to take place between two specific articles of the plurality of superimposed articles (predetermined separation point), while the other articles remain substantially undisplaced with respect to one another, the adhesion between the two specific articles is reduced compared with the adhesion between the other articles by measures suitable for reducing the friction coefficient between the two specific articles.
Measures for reducing the friction coefficient include treating at least one of the surfaces to be displaced relative to each other with a lubricant or smoothing it or positioning a sliding film between the articles to be displaced. Examples of lubricants are waxes, high-viscosity silicone oils or dry lubricants.
Building upon the teaching of the aforementioned patent, CH-534588 describes how a stack of flexible sheets is made separable at a plurality of different, predetermined points, by applying friction coefficient reducing measures to different, predetermined sheets in non-overlapping areas. The stack is separated at a specific one of the predetermined separation points by directing the displacement force to the corresponding treated area.
It has been found that the processes and the lubricants used in the methods according to CH-440339 and CH-534588 give satisfactory results in many applications. However, it has been found also that in other cases the reliability with which the displacement is effected exactly in the predetermined point is not adequate, so that the method cannot be used when high demands are made. Such cases include the separation of pages of multi-page printed products for the purpose of opening the product at a predetermined point. This is especially so when the individual pages of the printed products are made from a very smooth or correspondingly coated material and therefore adhere very little to one another, and/or when the individual pages of the printed products are made from different materials with different friction characteristics.
In a patent application of the same applicant and filed in parallel with the present application, a method for the separation of a plurality of at least partly superimposed, flat articles at a predetermined point is described. Using this method it becomes possible to solve separating problems in application areas in which the known methods cannot be applied, and/or to attain better results than are possible with the known methods.
An object of the present invention is to provide a composition for the treatment of surfaces of flat articles. The composition is to be used in the aforementioned method according to the parallel application, in order to produce the predetermined separation point.
The method described in the parallel application is based on the fact that the adhesion between superimposed, flat articles can be increased by static charging of their surfaces. According to the method of the parallel application, a static charge is produced on the surfaces of the superimposed, flat articles, by passing the articles through an electric d.c. voltage field oriented substantially perpendicular to the principal surfaces of the articles. Due to the effect of the field, dipoles are oriented or charges are displaced perpendicular to the principal surfaces and positive or negative charges are concentrated on the two surfaces of each of the articles. These charges cause electric attraction forces between the surfaces of superimposed articles and, therefore, increase the mutual adhesion.
The effect of the static charging of surfaces of superimposed, flat articles is reduced or prevented for at least one of two surfaces participating at a predetermined separation point, by treating the surface beforehand with an anti-static agent. Due to the limited conductivity of the anti-static agent, charges cannot concentrate on the treated surface or they are very rapidly compensated. Thus, passage through the voltage field causes no adhesion increase at the separation point or at least much less adhesion increase than it causes between non-treated surfaces. Therefore, the treated surfaces can be moved relative to each other by a lower force than is necessary for displacing non-treated surfaces, which displacement by low force distinguishes the separation point.
Application of a static charge for increasing the adhesion between flat articles not to be separated combined with a planned application of anti-static agent for suppressing the effect at a separation point can also be combined with the reduction of the friction between the flat articles to be separated by applying a lubricant, as described hereinbefore as prior art. Since for such a combination the anti-static agent and the lubricant are advantageously used on the same surface areas, the two agents can be applied and used simultaneously in the form of a mixture in a single method step. It is also possible to add a luminophore to the anti-static agent or to the mixture of anti-static agent and lubricant, the luminophore being useful for checking the separation at the predetermined separation point with the aid of luminescence sensors.
The composition according to the invention is a mixture comprising an anti-static agent and a lubricant. The mixture may comprise additional components such as a luminophore.